Elevator systems are in widespread use. Elevator systems are useful for carrying passengers, for example, between various levels within a building. Typical elevator systems include a machine comprising a motor and a brake for controlling the movement and position of the elevator car to provide the desired elevator service.
When an elevator car is stopped at a landing, the brake is utilized for holding the elevator car in the desired position. Various control techniques are known for releasing or lifting the brake.
For example, it is known to pre-torque the motor of the machine prior to lifting the brake to avoid any bouncing or jostling of the elevator car at the beginning of an elevator run. The load on the elevator car changes as passengers enter or exit the car, for example. Therefore, the possibility exists that the load on an elevator car is out of balance with the counterweight when the elevator car is about to depart from that landing. Any imbalance may cause the car to move vertically independent of movement of the motor when the brake is released. This may be experienced by passengers as a slight bump or jostle within the elevator car.
There are known techniques for pre-torquing the elevator machine motor to address such situations and avoid any undesirable car movement at the beginning of a run. One such technique is shown in U.S. Pat. No. 4,995,478. Such techniques typically rely upon measuring or detecting passenger load on the elevator car. There are known drawbacks associated with those techniques. Another technique is shown in U.S. Pat. No. 6,318,505. The technique in that document focuses on a brake that is applied directly to a guiderail, which is not the same as a machine brake.
Those skilled in the art are always striving to make improvements. It would be useful to have the ability to control the amount of torque on an elevator machine brake without depending upon a measurement of the load in the associated elevator car.